Synchronizing channel sharing with neighboring networks

ABSTRACT

The embodiments of the present invention provide a mechanism to synchronize centralized networks. Each centralized network includes a central coordinator controlling and managing network activities. The embodiments provide a way of allocating beacon slots, such that one of the beacon slots is synchronized to the alternating current line cycle and thus functions as a master timing sequence. In some embodiments, methods, devices, and systems are provided for detecting transmissions of non-coordinating networks.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/703,236 filed Jul. 27, 2005, entitled “Methodfor Sharing a Channel with Neighboring Networks,” which is herebyincorporated by reference herein for all purposes.

FIELD OF THE INVENTION

The present invention is related to multiple networks, particularly tochannel sharing between multiple networks.

BACKGROUND

In situations where multiple networks share a common communicationmedium or channel, the networks may compete for access to the channel,e.g., compete for bandwidth. In the absence of coordination betweenthese networks, they may interfere with one another, thereby reducingcapacity utilization and bandwidth available to stations within anynetwork.

SUMMARY

According to an embodiment of the present invention, a method ofsynchronizing one or more networks in a first group is provided. Each ofthe one or more networks, in the first group, includes a centralcoordinator adapted to operate in the uncoordinated operating mode or inthe coordinated operating mode. The central coordinator is furtheradapted to transition from the uncoordinated mode to the coordinatedmode or from the coordinated mode to the uncoordinated mode. This methodcomprises the steps of: allocating one or more beacon slots wherein eachbeacon slot is associated with a unique network from the networks in thefirst group; and transmitting at least one beacon at the allocatedbeacon slot by the associated network. The transmitted beacon includesnetwork allocation and scheduling information. Furthermore, one of theallocated beacon slots is a master slot that is synchronized to thealternating current (AC) line cycle thus functioning as a master timingsequence.

In another embodiment of the invention, a device is provided. Thisdevice comprises a beacon slot allocation module, an AC line cyclesynchronization module, a beacon decoding module, and a networkoperating module. The beacon slot allocation module is adapted toallocate one or more beacon slots, wherein each allocated beacon slot isassociated with one unique network that includes a central coordinator.Furthermore, the beacon slot allocation module is further adapted torelease one of the allocated beacon slots. The released beacon slot isadapted to be associated with another new network. The AC line cyclesynchronization module, on the other hand, is adapted to monitor the ACline cycle and to synchronize at least one of the allocated beacon slotsto the AC line cycle. Moreover, the beacon decoding module is adapted todecode one or more detected beacons; while the network operating modemodule is adapted to determine, based on at least one of the decodedbeacons, the network operating mode selected from the group consistingof coordinated mode and uncoordinated mode.

In another embodiment of the invention, a system is provided. Thissystem comprises one or more networks and a power line communicationnetwork medium operably coupled to the one or more networks. Eachnetwork in this system includes a central coordinator that controls itsnetwork. Each network operates in a mode selected from a groupconsisting of a coordinated mode and an uncoordinated mode. Furthermore,each of the central coordinator is adapted to allocate one or morebeacon slots within a beacon region, wherein each beacon slot isassociated with a unique network. Furthermore, at least one of the oneor more beacon slots is synchronized to an alternating current linecycle functioning as a master timing sequence.

In another embodiment of the invention, a method of synchronizing afirst centralized network and a second centralized network is provided.The first centralized network includes a first central coordinator and astation that is adapted to detect transmissions from the secondcentralized network. The second centralized network includes a centralcoordinator. The method includes the steps of monitoring, by thestation, for a transmission from the second centralized network within adetect time interval specified by the first central coordinator;reporting, by the station, after the specified detect time interval atleast one of the following: presence of the transmission; and absence ofthe transmission; and if absence of the transmission is reported,assigning, by the first central coordinator, the specified time intervalto the first station.

In another embodiment of the invention, a device that is adapted to beoperably coupled to a first centralized network is provided. The firstcentralized network includes a central coordinator. The device includesa detect-and-report procedure module and an input/output interface. Thedetect-and-report procedure module is adapted to receive one or moredetect time intervals; monitor for one or more transmissions from one ormore non-coordinating centralized networks within the received one ormore detect time intervals; and report to the central coordinator atleast one of the following: presence of the one or more transmissions,and absence of the one or more transmissions. The input/output interfaceis adapted to enable the device to communicate with the firstcentralized network.

In another embodiment of the invention, a central coordinator device isprovided. This device is adapted to be operably coupled to a firstcentralized network and a station. The device includes adetect-and-report procedure module and an input/output interface that isadapted to enable the device to communicate with the first centralizednetwork. The detect-and-report procedure module is adapted to transmit,to the station, a request to perform monitoring of transmissions fromnon-coordinating networks of the device, wherein the request comprisesone or more time intervals; receive a response indicating at least oneof the following: presence of the monitored transmissions, and absenceof the monitored transmissions; and allocate the one or more timeintervals to the station based on the received response.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings, and in which:

FIG. 1 is a high-level block diagram of an exemplary network accordingto an embodiment of the invention;

FIG. 2 is an exemplary group of networks according to an embodiment ofthe invention;

FIGS. 3A and 3B show exemplary beacons according to embodiments of theinvention;

FIG. 4 shows two exemplary beacons with compatible beacon structures,according to an embodiment of the invention;

FIG. 5 is an exemplary transition diagram illustrating how a network maytransition from a coordinated mode to an uncoordinated mode and viceversa, according to embodiments of the invention;

FIG. 6 shows exemplary beacons synchronized to an exemplary alternatingcurrent (AC) line cycle according to an embodiment of the invention;

FIG. 7 is a high-level exemplary flowchart showing how a networkoperating mode may be determined according to an embodiment of theinvention;

FIG. 8 shows exemplary beacons of two coordinating networks according toan embodiment of the invention;

FIGS. 9A, 9B, 9C, and 9D show exemplary beacons according to embodimentsof the invention;

FIG. 10 is a high-level exemplary flowchart showing how a new networkmay be established according to an embodiment of the invention;

FIG. 11 is another exemplary group of networks according to anembodiment of the invention;

FIG. 12 is an exemplary block diagram showing a number of beacon periodsdivided into a number of time intervals according to an embodiment ofthe invention;

FIG. 13 is a data flow of exemplary messages that are exchanged for adetect-and-report procedure according to an embodiment of the invention;and

FIG. 14 is a high-level block diagram of an exemplary centralcoordinator according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

To better understand the figures, reference numerals within the onehundred series, for example, 100 and 118, are initially introduced inFIG. 1, reference numerals in the two hundred series, for example, 200and 222, are initially introduced in FIG. 2, and so on and so forth. So,reference numerals in the eight hundred series, e.g. 804 and 820, areinitially introduced in FIG. 8.

FIG. 1 is a high-level block diagram of an exemplary network 100according to an embodiment of the invention. The network 100 is acentralized network (CN) that includes a central network coordinatoralso called the central coordinator (CCO) 120 that controls networkactivities, such as network timing, bandwidth allocation, and security,e.g., authentication and key management. For each centralized network100, there is typically one instance of a CCO 120 and zero or morestations/devices 110, 114, 118, 122. Any station (STA), however, mayfunction as the CCO provided it has the sufficient managementfunctionality. In some embodiments, the network is a power linecommunication (PLC) network. Stations that may be connected to this PLCnetwork include devices such as monitors, TVs, VCRs, DVDplayer/recorders, other audiovisual devices, computers, game consoles,sound systems, information appliances, smart-home technology appliances,home audio equipment, or any other device that is PLC-enabled orcompatible, or is able to communicate via the power lines. In anotherembodiment, the PLC network utilizes time-division multiplexingprocedures and technologies, such as TDMA. Although the embodiments ofthe invention herein are exemplified and discussed using power linenetworks, features of the present invention are also relevant to othernetworks; for example, but not limited to, networks that have acentralized architecture with a central coordinator controlling theactivities of the stations in the network. The use of power linenetworks in exemplary configurations is intended to aid in understandingthe features of the several embodiments of the invention.

In one embodiment of the invention, the network may use time divisionmultiplexing (TDM) as a method of multiple data streams sharing a signalaccording to time segments. The data streams may be reconstructedaccording to their time slots. In general, TDM enables severalusers/stations to share the same frequency by dividing it into differenttime slots. The stations transmit in rapid succession, one after theother, each using their own defined time slot. TDMA and TDM aretechniques known to those of ordinary skill in the art and may be usedwith PLC technology. The networks of the present invention may also useother time-division multiplexing technology, and other technology suchas orthogonal frequency-division or combinations and variations thereof.Other technologies supporting PLC, e.g., orthogonal frequency-divisionmultiplexing (OFDM), however, may also be used within the network.

FIG. 2 is a diagram showing an exemplary group 200 of networks 284, 286,288, 290, 292—e.g., similar to network 100 in FIG. 1, according to anembodiment of the invention. A network group 200 is typically acollection of one or more networks that have the same system timing,i.e., the beacon periods of these networks align with each other. Inanother embodiment, there may be two or more groups of networks, notshown, in the vicinity of each other.

A power line medium may be shared by multiple devices, which mayinterfere with each other. In some embodiments, each CCO typicallymaintains an Interfering Network List (INL). The INL of a CCO (or of acentralized network) typically contains the list of networks thatcoordinate with and interfere with the network controlled by the CCO. Insome embodiments, an assumption is made that if two CCOs are able todetect each other's beacon transmissions, the two networks controlled bythe two CCOs, including all their stations, interfere with each other.In some embodiments, the CCO of each network, for example at networkinitialization, determines its INL by decoding all existing beacons. TheCCO may also monitor existing beacons to update its INL, if appropriate,as existing neighboring networks are shut down and new neighboringnetworks are established.

In this exemplary group of networks 200, there are five exemplarynetworks 284, 286, 288, 290, and 292. Each network typically includesone central coordinator and zero or more stations. Exemplary network 1(N1) 284 includes a central coordinator, CCO1 202, and three stations204, 206, and 208; network 2 (N2) 286 includes CCO2 222 and threestations 224, 226, 228; network 3 (N3) 288 includes CCO3 242 and threestations 244, 246, 248; network 4 (N4) 290 includes CCO4 262; andnetwork 5 (N5) 292 includes CCO5 272 and three stations 274, 278, 282.Network 1 (N1), in this exemplary embodiment, has multiple neighbornetworks, i.e., N2 286, N3 288, N4 290, and N5 292. As another example,network 3 (N3) has neighbor networks N1 284, N2 286, N5 292, and N4 290.

In this exemplary group 200, N1 284 interferes with N5 292 and N2 286,i.e., CCO1 202 is able to detect the beacons of CCO5 272 and CCO2 222.Furthermore, N2 286 interferes with N1 284, N5 292, and N3 242; N3 288interferes with N4 290 and N2 286; and N5 interferes with N1 284 and N2286. Thus, in this exemplary embodiment, CCO1 202 has an INL thatincludes both N5 292 and N2 286. In one embodiment, informationcontained in the INL includes the network ID—an identifier that uniquelyidentifies the network—of that interfering network or CCO, the beaconslot or time slot number/ID with which the interfering network or CCOtransmits its beacon, and terminal identification information, such asaddress or temporary equipment ID, of the interfering CCO. In oneembodiment, a CCO within a group is able to request and exchange INLinformation with other CCOs within the group, and, optionally, outsideof the group. In another embodiment, network coordination is performedbetween interfering networks that are in the same group. In anotherembodiment of the invention, network coordination between interferingnetworks that are in different groups is optional.

In some embodiments, each CCO maintains its own topology table. Thistable may identify stations within the network, as well as the devicesthat those stations, including CCOs, are able to communicate and/ordetect. In some embodiments, the topology table may identify stations,including CCOs, from other networks that the devices are able tocommunicate and/or detect. The topology table may also maintaininformation about CNs present within and/or outside the system. Thistable is typically updated, e.g., periodically. The topology table mayalso include the INL. In general, the topology table providesinformation about devices, e.g., STAs and CCOs, and centralized networkswithin the system. The topology table may also include all STAsassociated and authenticated with the CCO. In some embodiments, it maycontain the MAC addresses of all STAs and the network identifiers of allnetworks detected by every STA associated and authenticated with theCCO.

Beacons:

In some embodiments, the CCO manages the activities of devices withinits network using, for example, beacons. Beacons are typically controlmessages that identify the frame configuration and the bandwidth (BW)assignments within a time frame to multiple networks and to deviceswithin a given network. Beacons are typically broadcasted by each CCO,e.g., as a multi-network broadcast, and are decoded by the stationswithin the network and, in some embodiments by the CCOs of neighbornetworks, including those that may be outside of the group. Beacons arealso typically tagged or identified, such that stations within a networkdecode and follow the BW allocation of their own network beacon and notthe beacon of another network. Beacons are also transmitted orbroadcasted, typically periodically, into the networks. They may also betransmitted unencrypted. In an alternative embodiment, beacons orportions thereof are encrypted. In general, a beacon may contain otherinformation, such as, but not limited to, MAC address of the CCO, checksum values, and management and control information.

FIG. 3A is an exemplary diagram of a beacon period for a network. Insome embodiments of the invention, a beacon comprises several parts orregions. Each region is further typically defined into one or more timeslots (e.g., 312, 314, 316, 320, 324, and 328). In some embodiments, abeacon comprises four regions:

Beacon Region:

In some embodiments, a beacon region 310A is the region wherein a CCO isable to transmit its own beacon. The beacon region generally includes aplurality of a certain number of beacons or time slots, with theduration of each beacon slot typically sufficient for the transmissionof a beacon. In one embodiment, the duration of each beacon slot isequal to the sum of the duration of a beacon PHY protocol data unit(PPDU) and the interframe space. A beacon region 310A, in oneembodiment, consists of one to a maximum number—typically defined withinthe system of time slots or beacon slots. In one embodiment, the size ofthe beacon region, including the number of time slots, may be adjusteddynamically by the CCO. In one embodiment, each CCO typically transmitsa beacon in one of the beacon slots—allocated for that CCO—within thebeacon region every beacon period. In one embodiment, information ordata about the beacon region and/or time slots within the beaconregion—for example, the number of beacon slots within the beacon region,the beacon slot ID that the CCO is using to transmit its current beaconprotocol data unit, and/or the start and/or end time—are kept by the CCOand/or by the CCO of the other neighbor networks.

In a typical embodiment, each CCO, in a group of networks, particularlythose in the coordinated mode, is associated with a distinct time slot,such that if there are five CCOs within a group, five time slots areallocated to transmit each of their respective beacons. In general,beacon slots are typically not reused, i.e., each beacon slot may beused by at most one network. This means that even if a CCO is able todetermine a beacon slot that it is able to transmit without collidingand with another network, for example, a beacon slot of anon-interfering network in the group, that beacon slot may not be used.For example, although N1 284 is not interfering with N4 290, in thisembodiment of the invention, CCO4 262 may not use the same beacon slotnumber used by CCO1 202 (see FIG. 2). Each CCO transmits at its ownunique associated or allocated time slot, facilitating identification ofthe transmitting CCO when a beacon is heard, for example, at aparticular time slot.

Furthermore, in a typical embodiment, the number of beacon slots in thebeacon region is the same for all networks in the coordinated mode thatare operating and that belong to the same group. If group coordinationis performed, coordinating networks that are in different groupstypically specify a sufficiently long protected region that overlapswith the beacon region of the other group.

In FIG. 3A, the beacon region includes five time slots, enabling each ofthe CCOs in the five networks, e.g., in FIG. 2, to transmit its ownbeacon. In this example, CCO2 222, CCO3 242, CCO5 272, CCO1 202, andCCO4 262 transmit their beacons at time slots B0 312, B1 314, B2 316, B3320, and B4 324, respectively. Each distinct or unique network in thegroup thus typically has its own defined time or beacon slot to transmitits beacon, regardless of whether the networks interfere with each otheror not. In one embodiment, the number of beacon slots may be increasedto accommodate new CCOs and networks.

In this embodiment, FIG. 3B is a variation of FIG. 3A, the beacon region310B is an exemplary variation of the above beacon region 310A andcontains a defined number of time slots, e.g., there are ten slotswithin the beacon region 310B. This defined number may be adjustedwithin the system. The time slots in the beacon region 310B, forexample, B5 322, B7, B8, and B9 326 are identified or tagged as beingunallocated or unused, and thus may be used by future or new incomingCCOs, if appropriate. The CSMA region 330B in FIG. 3B is shorter thanthe above CSMA region 330A.

In some embodiments, the number of beacon slots in the beacon region isa fixed rather than a variable number. In these embodiments, a limitednumber of messages or no messages are exchanged to enable neighbornetworks to operate in the coordinated mode. In some embodiments, thebeacon transmitted by each CCO contains information about the occupancyof the beacon slots in the beacon region. From this information, a newCCO may then determine a vacant beacon slot to transmit its new beaconin such a way that its beacon will not collide with that of its neighbornetworks. In some embodiments, a certain number of beacon slots may bereserved for the transmission of beacons. In other embodiments, thebeacons may be transmitted in any time interval or time slot that is notbeing reserved. In some embodiments, the fixed number of beacon slotsmay be defined by a user and may be altered, for example, upon systemreset or by a user changing a configuration file.

Carrier Sense Multiple Access (CSMA) Region or Contention Period (CP)Region:

The CSMA region 330A, 330B is a region wherein any one or more of manycontention access protocols are used to share the medium and tocoordinate network traffic. In some embodiments, a CSMA/CA protocol maybe used. A network may have one or more CP or CSMA regions. In oneembodiment, the CSMA or CP regions of one network do not overlap withthe reserved or contention-free period regions of other networks in itsINL. Communication, however, between two or more interfering networksmay be made during overlapping CSMA regions.

For each network, a “minimum CSMA region” (MinCSMARegion) immediatelyfollowing the beacon region is typically supported. The minimum CSMAregion, together with other CSMA regions, located elsewhere in thebeacon period, for example, may be used for the following:

-   -   Exchange of priority-based user data between STAs using CSMA,        e.g., CSMA/CA;    -   New STAs, including CCOs, to associate with the network;    -   Existing STAs to exchange management messages with the CCO        (e.g., to set up a new link);    -   New CCOs to exchange management messages to establish new        neighbor networks; and    -   Existing neighbor coordinators (NCCOs) to exchange management        messages with the CCO (e.g., to share bandwidth, or to change        the number of beacon slots).

Furthermore, in some embodiments, the allocation of a minimum CSMAregion immediately following the beacon region enables the beacon regionto increase or decrease in size without requiring a change in theschedule or locations in time within the frame, particularly ofcontention-free period time slots. Moreover, this enables new devicesjoining the centralized network to know where a CSMA region exists evenif they cannot hear other beacons. The new or joining station or devicemay then transmit network associate request messages, for example,messages requesting that the device be enabled to associate with thecentralized network, within this minimum CSMA region or time slot.

Reserved Region or Contention-Free-Period (CFP) Region:

This reserved or CFP region 340 is a period when only stations ordevices that have explicit authorization from the CCO are allowed totransmit. A reserved region is a time interval that is typicallyreserved by a network. The network that has been allocated or hasacquired control of the reserved region typically schedules thetransmission of its contention-free links here. In addition, the CCO mayalso schedule CSMA allocations that may be used only by the STAs in thatnetwork. For example, time slot 328 in the reserved region 340 has beenallocated by the CCO to STA A 114, so that STA A 114 may freely transmitat that time slot or interval 328 without interference, conflict, orcontention from other stations within the network. Explained in anotherway, in that time slot 328, STA A may freely transmit, while otherstations in that network or other neighbor networks in the group aretypically silent. This allocation is typically via beacons, such thatwhen a station decodes its own network beacon, information about whichstation is to use that time slot may also be defined within that beacon.In another embodiment, the CCO sends a message directly to the stationinforming that station when to transmit and sometimes even listen.

A network may have any number of reserved regions in a beacon period. Tobe compatible, other networks in its INL specify a stayout region in thesame time interval, thereby enabling the device with explicitauthorization to freely transmit. In one embodiment, it is possible tohave two non-interfering networks specify a reserved region in the sameinterval. This results in channel reuse with a higher total capacity.Referring back to FIG. 2, for example, considering that N1 284 does notinterfere with N4 290, N1 and N4 may, in one embodiment, both specify areserved region in the same time interval.

Stayout Region:

The stayout region 350 is a period within the time frame when allstations assigned a stayout region are instructed by the CCO to remainsilent, meaning no transmission. Typically, these devices are also notto use any contention access or contention-free access protocol. Astayout region is assigned to avoid conflicts with a device or thenetwork that has been assigned a reserved region in the same timeinterval. In general, a network specifies a stayout region if one ormore of the neighboring networks in its INL have specified a reservedregion or a protected region in the same time interval.

In some embodiments of the invention, information about beacon regions,including the number of time slots are kept within the system, typicallyby the CCO in each network. Information about beacon slot allocations inthe beacon region, as well as information about the other regions, inone embodiment, may be exchanged between CCOs. Furthermore, in someembodiments, the various types of regions need not be allocated in onecontiguous time interval. This means for example, that the various typesof regions may interleave each other, e.g., a time frame or beaconperiod includes a beacon region, followed by a CSMA region, followed bya stayout region, followed by another CSMA region, and then followed bya reserved region. The various regions within a beacon period may alsobe of varying sizes with varying number of time slot intervals ordurations. In one embodiment, the end time of each region type within abeacon period is stored, for example, in multiples of a definedallocation time unit (e.g., “AllocationTimeUnit”), e.g., 0.32 msec.

In another alternative embodiment, a beacon period may include anotherregion type (not shown) called a Protected Region. When a CCO detectsthe existence of another group with a different timing and if itoptionally decides to coordinate with networks in that group, that CCOtypically specifies a protected region in the same interval where thebeacon region of the other group is located. Stations in a networktypically are not allowed to transmit in a protected region. Groupcoordination, in one embodiment, is optional. A neighboring group ofnetworks, for example, may have a different beacon period start time.

In some embodiments, a network in uncoordinated mode has a beacon periodstructure that consists of a beacon region followed by a CSMA region,e.g., CSMA/CA region, optionally followed by one or more reservedregions and CSMA regions. Typically, the duration of the reservedregions and CSMA regions are carried in the beacon.

Based on the beacons transmitted by the CCO, the devices within anetwork are able to share bandwidth using the same medium or channel,e.g. power line medium. The CCO in each network thus typically controlsBW allocation and scheduling within its network. The stations within thenetwork thus decode their own network beacons, and accordingly performtheir functions, such as network transmission, following the beaconperiod allocations or schedule. In one embodiment, a beacon may alsocontain other or additional information, such as: a network identifierto identify the network; an alternating current (AC) line cyclesynchronized flag indicating whether the beacon transmission issynchronized or substantially synchronized with the AC line cycle; asource terminal identifier identifying the device transmitting thebeacon; a beacon slot ID identifying the beacon slot used by the senderof the beacon; beacon slot usage indicating the beacon slots used in thegroup; and handover-in-progress flag indicating whether the functions orsome of the functions of the CCO are being transferred to another CCO.

FIG. 4 shows exemplary beacons operating in one of the network operatingmodes; while FIG. 5 shows a transition diagram of network operatingmodes.

Neighbor Network Operating Modes—Uncoordinated Mode and CoordinatedMode:

A network typically operates in one of the following two modes—anuncoordinated (stand-alone) mode and a coordinated mode. In theuncoordinated mode, a new CCO typically establishes a new network inuncoordinated mode if it is unable to detect any beacons. This mayhappen either because there are no existing neighbor networks in thevicinity of the new CCO or because there are existing networks but thenew CCO is not able to detect any of the beacons. In this mode, qualityof service (QoS) may still be provided by allocating reserved orcontention-free allocations or time slots to applications that mayrequire QoS. In some embodiments, a threshold or conditions have to besatisfied before a CCO is able to say that beacons are detected, e.g.,beacons have to be detected reliably, i.e., have to be detected acertain number of times within a certain time period or cycle. Thus, insome embodiments, if beacons are not detected satisfying a certaincondition, the new CCO establishes a new network in uncoordinated mode.A CCO operating in uncoordinated mode, in some embodiments, generatesits own timing and transmits its periodic beacon independently of othernetworks.

In the coordinated mode, a new CCO typically establishes a network inthe coordinated mode if it is able to detect beacons typically reliablyfrom at least one existing network. The new CCO may acquire the timingof the existing network and join the existing network to form a group.In the coordinated mode, a network may typically share bandwidth withneighboring networks in its INL, such that QoS may be provided withineach network by using reserved or CFP regions.

In the coordinated mode, the regions of the beacon of a network aretypically compatible with the regions of other networks in its INL. Forexample, if one network in the group, e.g., N1 284, specifies a reservedregion and another network in its INL, e.g., N2 286, specifies a stayoutregion in the same interval, the two schedules are said to becompatible. On the other hand, if a network specifies a reserved regionand a network in its INL specifies a CSMA region, they are said to beincompatible. Table I below shows the typical interaction between thedifferent regions, typically when the CCOs are in the coordinated mode.

TABLE I Neighbor CCO That Neighbor CCO That Hears The Owner CCO HearsThe Owner CCO And Is In The Same But Is In A Different Owner CCO GroupGroup Beacon Beacon Protected Protected Protected or Stayout BeaconReserved/CFP Stayout Stayout CSMA/CP CSMA or Stayout CSMA or Stayout

FIG. 4 shows two exemplary beacons 460, 470 for two coordinating CCOs,for example, CCO1 202 and CCO5 272, respectively. The top beacon 460 andthe bottom beacon 470 show an exemplary BW allocation and scheduling fornetwork 1 284 and network 5 292, respectively. In this embodiment, N1284, along with CCO1 202, and N5 292, along with CCO5 272, arefunctioning in the coordinated mode. To be compatible, when CCO1schedules its beacon region 462, the neighbor network CCO5 alsoschedules its beacon region 472. Similarly, when CCO1 schedules a CSMAregion 464 for channel contention, CCO5 also schedules a CSMA region 474and a stayout region 482. In one embodiment, CCO5 may schedule an entirestayout region or CSMA region to correspond to the CSMA region 464. WhenCCO5 schedules a reserved region 476, CCO1 schedules a correspondingstayout region 466 so that the devices allocated reserved time slots 476during those time intervals are able to transmit. Similarly, when CCO1schedules a reserved region 468, CCO5 schedules a stayout region 478 toalso guarantee, for example, QoS for network 1. In some embodiments, aminimum CSMA region (not shown) is allocated immediately following abeacon region.

FIG. 5 is a transition diagram illustrating how a network generallytransitions between the typical two network operating modes—thecoordinated mode 590 and uncoordinated mode 594. A new CCO that ispowered on 502 and is unable to detect, e.g., reliably, any existingnetworks 508, starts operations in the uncoordinated mode 594. A CCO,however, that is able to reliably detect one or more beacons startsoperating in the coordinated mode 506. In general, a CCO remainsoperating in its operating mode 562, 572, unless certain conditions 528,532 trigger a CCO to transition to the other network mode. A CCO mayalso power off or leave the network or group 518, 522, as shown.

Transition to Uncoordinated Mode

A CCO typically functions in the coordinated mode 590 when it is able todecode other beacons reliably. If all the networks in the CCOs INL haveshut down or if the CCO is no longer able to detect any other beaconsfor several beacon periods, typically, all in a row, the CCO assumesthat the other networks have been powered off, and thus the CCOtransitions 528 to the uncoordinated mode 594. The number of beaconperiods determining whether a CCO may assume that all the other networkshave been powered off may be predefined, user-defined, or dynamicallydefined within the system.

Transition to Coordinated Mode

A CCO typically functions in the uncoordinated mode 594 when it does notdetect any other beacons. If that CCO receives a notification, such as anew CCO is confirming that a new network is going to be set-up or theCCO is now able to detect other beacons 532, the CCO then transitionsfrom the uncoordinated mode 594 to the coordinated mode 590.

Another exemplary trigger for a transition from uncoordinated mode 594to coordinated mode 590 is when the CCO receives a dummy beacon messagefrom another CCO 528. A dummy beacon in general is used to coordinatebetween multiple beacon regions. This trigger generally occurs whencoordination between networks from different groups are performed. Thismay happen, for example, when the new CCO establishes a new network inuncoordinated mode, because the new CCO is unable to detect any existingnetworks because of interference, and therefore did not specify aprotected region to protect the beacon region of an existing networktypically in a different group. When the existing network receives thenew beacon from the new CCO, the existing network typically sends adummy beacon message to announce its own existence. The new CCO may thentransition to coordinated mode 590 and may also accordingly specify aprotected region to protect the beacon region of the existing network ina different group.

Neighbor network coordination are further explained in the followingpending applications with the following Ser. Nos. 11/089,792 entitled“Systems and Methods for Network Coordination with Limited ExplicitMessage Exchange,” 11/089,756 entitled “Method for Transitioning betweenCoordination Modes for Interfering Neighbor Networks,” and 11/089,882entitled “Methods and Systems for Network Coordination.” These pendingapplications are herein fully incorporated by reference.

AC Line Cycle Synchronization in Coordinated Mode

In one typical embodiment of the invention, the location of the beaconis synchronized with the AC line cycle. In this embodiment, performanceand QoS stability in the presence of power line noise may be improved.Beacon periods may be synchronized with the underlying AC line cyclefrequency, for example, with the 50 or 60 Hz AC line cycle. In oneexemplary embodiment, when operating in power line environments with anAC line cycle frequency of 60 Hz, the beacon period may be set, forexample, to 33.33 msec. On the other hand, a beacon period, for example,of 40 msec may be used when operating over 50 Hz AC line cycle. Theabove exemplary beacon periods correspond to typically twice theunderlying AC line cycle period. In some embodiments, beacons may besynchronized with respect to the AC line cycle, for the uncoordinatedmode, coordinated mode, or both.

In some embodiments, synchronizing beacon transmission to the line cycleenables better channel adaptation (e.g., tone maps)—for example, lessadjustments. CCOs may phase lock the beacon transmission to the AC linecycle to provide synchronization for all stations in the network.Line-cycle synchronization may be achieved by having a CCO track aparticular point in the AC line cycle, for example, from zero crossing,using in one embodiment, a detector, including a digital phase lockedloop (DPLL) or equivalent. Thus, in one embodiment, a CCO may phase lockthe beacon transmission to the AC line cycle to provide synchronizationfor all stations in the network.

A CCO may also use its local tracking history to also predict futurelocations of beacons and announce this to all stations in the beaconschedule, e.g., be able to announce the location of the beacon over thenext few beacon periods. To ensure that stations with persistentallocations, i.e., valid for a certain number of periods, may transmiteven when a beacon is not detected, a CCO may provide information aboutthe location of future beacons within a beacon payload, for example.

In a group of coordination mode networks, the CCO in the smallestoccupied beacon slot number typically tracks the AC line cycle andprovides the beacon transmit offset information to other coordinatingCCOs in that coordinating group. In some embodiments, the beacontransmit offset is fixed and is typically changed when the beacon isrelocated. In some embodiments, the beacon period start time issynchronized to the AC line cycle. In some embodiments, the CCO may alsoset an AC line cycle synchronized flag in the beacon to indicate that itis locally tracking the AC line cycle. All other coordinating CCOs inthe group thus may track a CCO that is reliably detected and that hasthe largest beacon slot number that is smaller than the beacon slot ofthe current CCO.

To ensure that the group of network operations does not get disruptedwhen a coordinating CCO shuts down, in one embodiment, a departing CCOmay use an AC line synchronization (“synch”) count down field, forexample, that indicates the beacon period in which it stops transmittingthe beacon. In one embodiment, the AC line sync count down field is usedto indicate the number of beacon periods in which the AC line cyclesynchronization of the current CCO is going to change.

If a new CCO joining a group of CCOs in coordinated mode determines thata beacon slot number smaller than the beacon slot of the CCO that iscurrently tracking the AC line cycle is not used, in some embodiments,the new CCO may request that smaller beacon slot number if the beacon ofthe CCO currently tracking the AC line cycle is detected, typically withsome reliability threshold. In this embodiment, when the new CCO becomespart of the group and starts transmitting its beacons, the new CCOtypically also initially tracks the AC line cycle information providedby the CCO transmitting the beacon in the larger beacon slot number andcurrently tracking the AC line cycle. Once a CCO that is tracking the ACline cycle determines the presence of a beacon in a smaller beacon slotnumber, it generally handovers or transfers the AC line cyclesynchronization function to the CCO occupying the smaller beacon slotnumber by typically using the AC line sync count down field whichindicates the number of beacon periods when that CCO is going to stoptracking the AC line cycle and when the other CCO is going to starttracking the AC line cycle.

In another embodiment, the beacon structure typically of a group may berelocated to a different part of the AC line cycle. This relocation mayin one embodiment be performed by having a relocation count down fieldthat indicates the number of beacon periods after which the beaconrelocation may occur. Another field that may be used in conjunction withthe relocation count down field is a relocation offset field (RLO). Insome embodiments, an RLO field is a field that indicates the offset ofthe new beacon location from the current beacon location. In someembodiments, the RLO field is defined in multiples of 0.32 msec.Typically, the relocated beacon is delayed in time relative to the oldbeacon location.

FIG. 6 is an exemplary AC line cycle illustrating how the beacon slotsmay be synchronized. In the following example, refer collectively toFIGS. 2, 3A, and 6, with the group 200 of five exemplary networks N1284, N2 286, N3 288, N4 290, and N5 292 where all are functioning in thecoordinated mode and each is assigned its own beacon slot to transmitits beacon. Beacon slots B0 312, B1 314, B2 316, B3 320, and B4 324 areassigned to CCO2 222, CCO3 242, CCO5 272, CCO1 202, and CCO4 262,respectively. CCO2 222 accordingly occupies the smallest beacon slotnumber, B0 312, and transmits, at an offset 640 from a point in the ACline cycle, e.g., the zero crossing, at B0 604. In some embodiments, thebeacon transmit offset is zero, meaning that the smallest beacon slot istransmitted at the zero crossing. The next CCO, CCO3 242, occupying thenext occupied time slot, B1 608, for example, then transmits at adelayed time from B0 604, typically delayed by a duration 630 equal tothe size of the beacon slot and the beacon interframe space, if any. Thetiming of CCO2, occupying the first or lowest occupied or allocatedbeacon slot number—B0 604, thus is a master beacon slot that functionsas a master timing sequence, synchronizing when the other coordinatingCCOs are to transmit their respective beacons.

Typically, a CCO bases its timing on a beacon that it is able to detect.In some embodiments, a CCO, e.g., CCO3, tracks the timing of the largestbeacon slot number, which it is able to detect that it is smaller thanthe beacon slot of CCO3, in this case, B0 604, i.e., CCO2. CCO 5 in turnbases its beacon transmission from the beacon that CCO5 is able todetect which has the largest beacon slot number that is smaller than thebeacon slot of CCO5, i.e., bases its timing from B0 604, i.e., CCO2 Inthis exemplary embodiment, CCO5 is able to detect the beaconstransmitted by CCO1 but not those transmitted by CCO3. CCO 5 transmitsat B2 612 after a time delay. CCO1 then bases its beacon transmission616 from B2 612, i.e., CCO5, and CCO4 bases its beacon transmission 620from B1 608, i.e., CCO3. The beacon period is thus synchronized to theAC line cycle thereby synchronizing also the neighbor networks ingeneral.

The beacon slot B0 thus functions as a master slot that defines a mastertiming sequence from which the other beacon slots base their timing. Insome exemplary embodiments, the transmission of the other beacon slotsis based on the master slot and, optionally, one or more offsets. Thedelayed time duration may in one embodiment be presented as an offsetfrom the previous beacon slot being tracked. In an alternativeembodiment, a fixed constant of time is used to define the delay. In oneembodiment, a data structure containing offset values from one beacon toanother is stored and maintained by one or all of the CCOs. In anotherembodiment, the offset is defined as a beacon transmission offset field,which may contain a signed 16-bit value measured in units of the CCOclock period, e.g., based on the CCO's 25 MHz clock. In anotherembodiment, such offset field is defined as a multiple of a certain timeperiod, e.g., multiples of 0.32 μsecs. In another embodiment, offset offuture beacons from their expected location, e.g., for relocation, mayalso be maintained and announced within the system. In anotherembodiment, a bit mask or map, e.g., called slot usage, is used to keeptrack of occupied/allocated beacon slots, such that bits that are set to“1” indicate beacon slots that are used by CCOs and bits that are set to“0” indicate unoccupied beacon or time slots. Various other softwareengineering techniques, such as to store AC line information, may beused as known to those to those of ordinary skill in the art.

FIG. 7 is a high-level exemplary flowchart illustrating a process bywhich a CCO may determine its network operating mode. Typically, only aCCO (or a STA that is CCO-capable) is able to establish a network. Thus,if a STA, that is a non-CCO-capable device, joins a group, it generallyjoins as one of the stations in a network and is controlled by a CCO.The STA's function as a station includes decoding and following beaconschedules rather than generating and transmitting beacons to control thenetwork. The exemplary flowchart of FIG. 7 accordingly illustrates aCCO-capable STA/CCO determining its network operating mode.

In the first operation, a CCO connects with the communication ortransmission medium, for example, plugging the CCO device into anelectric outlet and powering it up (step 704). When the CCO is connectedto the medium, it listens for beacons (step 708). If no networks existor no beacons are detected (step 712), the CCO establishes a new networkin uncoordinated mode (step 732). If networks, however, already exist,meaning that beacons from networks are heard (step 712), the CCO thenrequests association with one of the networks (step 716). In oneembodiment, not shown, if more than one group exists, the CCO firstdecides which group to associate or join. In general, the CCO associateswith typically one network but may request association from some or allthe networks that the CCO hears, until it is accepted by one of thenetworks. If the CCO is able to associate with one of the networks (step720), that CCO becomes part of that network and is typically associatedas a station, rather than as a CCO (step 724). This means that the CCOin that network functions as a STA controlled by the CCO alreadycontrolling that network. The CCO/STA, however, may be designated as abackup or auxiliary CCO, if appropriate. In one embodiment, a CCOcreates a new network or neighbor network only if it fails to associatewith existing networks, for example, in situations where the CCO doesnot possess the network password, for example.

If the CCO, however, is not able to associate with any of the existingnetworks, the CCO determines if there are available beacon slots (step738) so as to establish a new neighbor network in the coordinated modewithin the group. In a typical embodiment, this may be determined bydecoding beacons and determining vacant beacon slots. If there is anavailable beacon slot for that CCO to use to transmit its own beacon inthe group, the CCO establishes a new network in the coordinated mode andjoins the group (step 742). On the other hand, if the beacon region hasall available beacon slots allocated for other CCOs, the CCO establishesa new network in the uncoordinated mode (step 732). In some embodiments,the CCO in the uncoordinated mode detects the beacon of other networksand determines, for example, an idle interval using CSMA and startstransmitting its beacons in that interval once every beacon period. Insome embodiments, the CCO in the uncoordinated mode may maintain its owntiming and decide its schedules independently, and thus be in adifferent group. In another embodiment, the beacon period timing of theuncoordinated mode is different from the beacon period timing of thoseCCOs operating in the coordinated mode typically so as to avoidcollision with the CCOs operating in the coordinated mode. As shown inFIG. 5, a CCO or network may transition from uncoordinated mode tocoordinated mode and vice versa.

Establishing a New Network in Coordinated Mode

In one exemplary embodiment, in order to establish a new network in acoordinated mode, the CCO, i.e., a new CCO, typically assigns a shortnetwork identifier (SNID) to identify itself, finds a vacant beacon timeslot in the beacon region to use, and specifies a beacon periodstructure that is compatible with all the networks that are in its INL.

Determining the Interfering Network List and Choosing an SNID.

The new CCO first requests the INL of the neighbor CCOs. This stepenables the new CCO to ascertain the SNID and network identifier (NID)of the interfering networks of the neighbor CCOs. The new CCO may thenrandomly choose a SNID value, which is not used by any of its neighborCCOs or by any interfering networks of its neighbor network CCOs. Themanner in which the SNID is assigned, however, may be varied, forexample, choosing a SNID from a table or generalism of random SNIDs.Table II below shows an exemplary message, including exemplary fieldsthat may be included in a message that may be used by a CCO to requestthe INL of another CCO. This message is typically sent unencrypted.

TABLE II Exemplary Request for Interfering Network List (e.g.,NN_INL.REQ) Field Brief, Exemplary Definition MyTEI TEI of the sender ofthis message. MySNID SNID of the sender of this message. MyNID NID ofthe sender of this message. MyNumSlots Number of Beacon slots in theBeacon Region of the sender of this message. MySlotID SlotID where thesender of this message transmits its Beacon NumInfo Number of networkinformation to follow (=N) SNID_1 SNID of the first network that thesender can detect. NID_1 NID of the first network that the sender candetect. NumSlots_1 Number of Beacon slots in the Beacon Region of thefirst network that the sender can detect. SlotID_1 SlotID where thefirst network that the sender can detect transmits its Beacon. Offset_1Offset between the Beacon Regions of the sender of this message and thefirst network that it can detect, measured in units ofAllocationTimeUnit, e.g., 10.24 μsec. Offset = e.g., start time ofsender's Beacon Region minus start time of receiver's Beacon Region(modulo) Beacon Period. . . . . . . SNID_N SNID of the last network thatthe sender can detect. NID_N NID of the last network that the sender candetect. NumSlots_N Number of Beacon slots in the Beacon Region of thelast network that the sender can detect. SlotID_N SlotID where the lastnetwork that the sender can detect transmits its Beacon. Offset_N Offsetbetween the Beacon Regions of the sender of this message and the lastnetwork that it can detect, measured in units of AllocationTimeUnit.Finding a Vacant Beacon Slot.

CCOs generally broadcast time-slot scheduling using beacons. Todetermine a vacant beacon time slot, the new CCO decodes existing orbroadcasted beacons to determine the beacon region structure of eachnetwork in its INL, which is typically also the group that the CCOchooses to join. Moreover, the CCO determines a common beacon slotindicated as available or “free,” by all networks. If a vacant commonbeacon slot cannot be found, the new CCO may propose to use a new beaconslot, typically subject to the maximum limit of the number of maximumbeacon slots available in a beacon region.

Specifying a Compatible Beacon Period Structure.

After determining the SNID and a common vacant beacon slot, the new CCOthen typically sends to all neighbor CCOs in its INL, a request toset-up a new network or CN, using the SNID and the determined orproposed beacon slot time. In one embodiment, this request is sentunencrypted and in a CSMA region of the neighbor CCO. If the request isgranted by a neighbor CCO, that neighbor CCO also sends its beaconperiod structure or schedule to the new CCO. If one neighbor CCO rejectsthe request to start a new network/CN, the request is cancelled for allneighbor CCOs. Assuming, however, that all of them accepted or grantedthe request, the new CCO, typically basing on all the schedules receivedfrom the various neighbor CCOs, determines a compatible beacon periodstructure for it to use as a CCO of a new CN. This determining steptypically enables the channel, particularly the bandwidth, to be sharedbetween the new centralized network and the existing neighbor networks.

In some embodiments, if the proposed beacon slot is not available ordoes not exist, the neighbor CCOs in the group typically increase thesize of their beacon region, including the number of beacon slots. Thechange in the number of beacon slots is typically broadcasted via one ormore beacons. Each neighbor CCO in the same group may also implicitly orexpressly request neighbor CCOs in a different group to appropriatelyincrease the duration of their protected region or create a newprotected region, assuming group coordination is performed.

Determining a Compatible Beacon Schedule

Uncoordinated Mode: In one embodiment, a new CCO may establish a newnetwork in uncoordinated mode. This new CCO typically specifies a beaconregion with one beacon slot and a CSMA region for the remaining of thebeacon period. In one embodiment, if it cannot detect other beacons, itmay optionally establish one or more CFP or reserved regions.

Coordinated Mode: Alternatively, if the new CCO joins an existing groupof networks in coordinated mode, the new CCO schedules its beacon suchthat it is compatible with the schedules of the existing networks in itsINL. Typically, the CCO determines the INL and the INL allocation. Basedon the INL allocation, a compatible schedule is set-up. To determine theINL allocation, a CCO typically decodes the beacons of all the networksin its INL and computes or determines the combined effect of theirallocations, i.e., the INL allocation. For example, if one neighbornetwork in the INL specifies a reserved region and another neighborspecifies a CSMA or stayout region, the resultant INL allocation is areserved region, because a reserved region “outweighs” both CSMA andstayout regions. In another example, if three networks have threedifferent region types in the same time interval allocation, e.g.,reserved region, CSMA region, and stayout region, the determined INLallocation is the reserved region, because the reserved region outweighsboth the CSMA and the stayout regions. In general, the INL allocation isassigned the same region type of the network whose region type ishighest in an exemplary hierarchy. Table III below in general shows anexemplary hierarchy of the various regions of a beacon period.

TABLE III Hierarchy of Regions Level of Weight (5 = Most Weight, 1 =Least Weight) Region Type 5 Beacon Region 4 Protected Region (generally,present if coordinating between groups) 3 Reserved or CFP Region 2 CSMAor CF Region 1 Stayout Region

In a typical embodiment, the start and/or end time of each region isalso generally maintained or kept track of by the various CCOs, so thatan appropriate compatible schedule and INL allocation may be determined,particularly when regions are of varying sizes or allocations and/or ifthere are differences in system timing.

Table IV below shows exemplary results of INL allocation based on thehierarchy shown in Table III. In this exemplary table, there are twoneighboring networks, Network 1 and Network 2.

TABLE IV Exemplary INL Allocation Region Type Region Type of INLAllocation of Network 1 Neighbor 2 of Networks 1 and 2 Beacon Beacon,Protected, Reserved, Beacon CSMA or Stayout Protected Beacon BeaconProtected Protected, Reserved, CSMA, or Protected Stayout Region TypeRegion Type of INL Allocation of Network 1 Neighbor 2 of Networks 1 and2 Reserved Beacon Beacon Reserved Reserved, CSMA, or Stayout ReservedCSMA Protected Protected CSMA CSMA or Stayout CSMA Stayout CSMA CSMAStayout Stayout Stayout

Once the INL allocation is determined, the CCO typically complies withthe conditions outlined below, to be compatible. (See FIG. 4, forexample, for compatible beacon schedules.) Initially, the new CCO doesnot specify any reserved regions.

-   -   i.) If the INL allocation is a beacon region and is the first        entry in the beacon period, the new CCO typically specifies a        beacon region. However, if it is not the first entry, the new        CCO typically specifies a protected region, where the        coordination between groups of network is in effect. In some        embodiments, there is typically only one beacon region within a        beacon.    -   ii.) Otherwise, if the INL allocation is a protected region or a        reserved region, the new CCO specifies a stayout region.    -   iii.) Otherwise, the new CCO specifies a CSMA region in all        other intervals.

Once a network is established in coordinated mode, the conditionstypically used by an existing CCO to set the subsequent region types areas follows:

-   -   i.) If the INL allocation is a beacon region and if it is the        first entry, the existing CCO specifies a beacon region.        However, if it is not the first entry, the existing CCO        specifies a protected region, where the coordination between        groups of network is in effect.    -   ii.) If the INL allocation is a protected region or a reserved        region, the existing CCO specifies a stayout region.    -   iii.) If the INL allocation is a CSMA region, the existing CCO        specifies a CSMA region.    -   iv.) If the INL allocation is a stayout region, the existing CCO        may specify a CSMA region or a reserved Region.        New Network Instantiation amid Two Groups of Networks

FIG. 8 shows exemplary beacons 810, 820, 830, particularly their beaconregions or portions thereof. A new CCO may detect two or more groups ofnetworks in the vicinity of each other. In this exemplary embodiment,two existing networks, NCO1 810 and NCO2 820, are unable to detect eachother's beacons, and there is a fixed time offset 826 between theirbeacon period boundaries. The new CCO, however, is able to detect anddecode the beacons from both NCO1 and NCO2. The top beacon 810 shows thebeacon structure of NCO1 and typically also its group. In this beacon,NCO1 transmits its beacon at beacon slot #0 804, e.g., SLOTID=0; NetworkNCO1, particularly its CCO, transmits its next beacon at the next beaconslot #0 808, i.e., at the next beacon period. The second beacon 820shows the beacon structure of NCO2 and typically also its group. NCO2transmits at slot #0 824. The next beacon transmission is at the nextbeacon period slot #0 828.

Considering that the timings of the two existing networks aredifferent—two different groups, the new CCO typically acquires thetiming of one of the groups. If the new CCO chooses the same timing asNCO1, meaning joins NCO1's group, the new CCO typically exchangesmessages with NCO1, particularly messages requesting to create a newnetwork in the coordinated mode, including a new beacon slot allocation,e.g., SLOT #1, for the new CCO. In this embodiment, the new networkestablished by the new CCO and the network of NCO2, however, mayinterfere with each other because they do not coordinate with eachother.

In another exemplary embodiment, to coordinate with another group with adifferent timing, the new CCO may optionally exchange the request tocreate a new network with NCO2, in addition to the request to NCO1. Therequest to NCO2, in one embodiment includes an offset field, e.g.,offset 826, which may be set to a non-zero value to indicate that thenew CCO has a different system timing than NCO2. This offset field maycontain the time offset between the beacon regions of the sender and thereceiver, typically in units of a defined allocation time unit. If NCO2accepts the request of the new CCO, all three networks may coordinatewith each other. In this embodiment, the new CCO may specify a protectedregion 838 in the same interval where NCO2 has specified a beacon regionfor that NCO2 group.

The bottom beacon 830 shows an exemplary beacon structure, after the newCCO joins NCO 1's group in the coordinated mode and with groupcoordination. The new CCO is allocated a beacon slot, e.g., slot #1 834,at which the new CCO may transmit its beacon. The next beacontransmission for the new CCO is typically in the same slot number 842,slot #1, for example.

FIGS. 9A, 9B, 9C, and 9D show exemplary beacons according to embodimentsof the invention. In this exemplary embodiment, FIG. 9A, network Ainitially operates in the uncoordinated mode. The exemplary beaconstructure or portion thereof of network A before network B joins thegroup, is shown at the top beacon 902. This beacon 902 indicates thatCCO A transmits its beacon at slot #0 904 and that there is only onebeacon slot in the beacon region.

For illustrative purposes, CCO B wants to join network A and toestablish a new network, FIG. 9B. CCO B typically performs this functionby sending a request to establish a new network to CCO A. This request,e.g., called NN_NEW_NET.REQ in this example, is typically a message sentby a new CCO to the CCOs in its INL to request to set up a new network.This request to establish a new network may contain a proposed beaconslot number, a proposed number of beacon slots, and a time offsetbetween the beacon region of the sender and the receiver. In someembodiments, a field, for example, an offset field is set to zerosindicating that the message/request is sent by a CCO of the same group,i.e., with the same system timing. Otherwise, the offset field may bedefined as the start time of the beacon region of the sender minus thestart time of the beacon region of the receiver. In one embodiment, themessage is sent unencrypted. When CCO A receives this request toestablish a new network from CCO B, CCO A typically increases its beaconslot by one and typically sends a confirming response message, e.g.,called NN_NEW_NET.RSP in this example, to CCO B indicating success, ifappropriate.

After receiving the NN_NEW_NET.RSP message indicating success, forexample, CCO B may then send another message, e.g., calledNN_NEW_NET.CNF in this example, to CCO A to confirm the establishment ofthe new network in coordinated mode. An exemplary NN_NEW_NET.CNFmessage, in one embodiment, is sent by a new CCO, typically the CCO thatalso sent the NN_NEW_NET.REQ message, to the CCOs in its INL to confirmwhether the request to establish a new network is going to proceed or becanceled. The beacon structures of network A 908 and network B 916,after network B joins the group, in this example show that the beaconregions of both network A 908 and network B 916 contain two slots,beacon slot #0 912 allocated for network A beacon transmission and slot#1 920 allocated for network B.

Slot Usage

In some embodiments, a slot usage field 918, 922 is an 8-bit bit mask orbit-map. Each bit typically corresponds to a slot number, and a “1” inthat bit indicates that the slot is occupied or allocated while a “0”indicates not used or unallocated. Other software engineering techniquesas known to those of ordinary skill in the art may be used to indicateslot usage, such as having an array of fields.

In some embodiments, a CCO in coordinated mode typically sets the slotusage field according to the following exemplary rules:

-   -   (a) Set to “1” the bit corresponding to the beacon slot where        the CCO transmits its own beacon;    -   (b) Set to “1” the bit corresponding to the beacon slot where        beacons of a network, of the same group, in the CCOs INL are        detected; and    -   (c) Set the remaining bits to “1” if the same bit is set to “1”        in one or more beacons of a network in the CCOs INL, except if        the CCO has received a message indicating that such bit is to be        set to “0.”

Referring to FIG. 9C for further illustration, by example, shouldanother new CCO, CCO C, decide to establish a new neighbor networkwithin the same group of networks A and B. In this embodiment, CCO C isable to decode beacons from network B but is unable to decode beaconsfrom network A. The beacon of network B, for example, its slot usagefield, 918 (FIG. 9B) indicates that the first two beacon slots areoccupied. In this example, CCO C sends an NN_NEW_NET.REQ message to CCOB requesting to use a new beacon slot, e.g., the third slot in thebeacon region, i.e. slot ID=2 or slot #2. When CCO B receives thismessage, it typically first coordinates with the networks in its INL,i.e., network A, to increase the size of the beacon region. To do this,CCO B typically sends a message to CCO A, e.g., NN_CHG_BR.REQ, torequest that the number of beacon slots be increased to three. CCO Athen replies to CCO B with a message containing a successful resultcode. In one embodiment, if CCO A and CCO B are in different groups, theNN_CHG_BR.REQ message may implicitly or expressly request CCO A tochange the duration of its protected region. When CCO B receives thereply from CCO A, it sends an NN_NEW_NET.RSP message to CCO C to acceptits request to start the new neighbor network.

Continuing with this example, CCO C then sends an NN_NEW_NET.CNF messageto CCO B to confirm the establishment of a new network. The threebeacons 924, 928, 932 (FIG. 9C) show the beacon regions of network A,network B, and network C. The slot usage fields 936 are updated toindicate that all three beacon slots are occupied, even though CCO C isnot able to detect the beacons of network A in slot ID=0. In thisexemplary embodiment, networks A, B, and C are functioning in thecoordinated mode.

A new CCO, CCO D, may then decide to start a new neighbor network (FIG.9D). CCO D, in this example, is only able to decode beacons from networkC. The beacon slot usage field of network C, at this point, indicatesthat the first three beacon slots are occupied—“111.” CCO D accordinglysends an NN_NEW_NET.REQ message to CCO C requesting to use Slot ID=3,which is the fourth slot in the beacon region 942. When CCO C receivesthe message, it first typically coordinates with the networks in itsINL, i.e., network B to increase the beacon region size. CCO C may thensend an NN_CHG_BR.REQ message to CCO B requesting to increase the numberof beacon slots to four. CCO B then typically first exchangesNN_CHG_BR.REQ/RSP messages with CCO A and then sends an NN_CHG_BR.RSPmessage to CCO C.

CCO C then replies with an NN_NEW_NET.RSP message, for example,accepting the request of CCO D. CCO D then typically sends anNN_NEW_NET.CNF message to CCO C confirming the establishment of the newnetwork. The four bottom beacons 950 show the beacon region of eachnetwork after network D has established a new neighbor network.

A CCO of the present invention typically is able to share bandwidthbetween neighbor networks. In general, a CCO, for example, may requestadditional bandwidth with neighbor networks in a coordinated mode. TheCCO may do so by sending a request, to the various CCOs of the neighbornetworks, indicating the time slots that the CCO wants to reserve. Ifthe request is granted by all neighbor CCOs, the requesting CCOaccordingly changes its beacon structure, for example, allocating thoserequested time slots to a CFP. To be compatible, however, the neighborCCOs modify their time slots to a stayout region.

Sharing Bandwidth in Coordinated Mode:

FIG. 10 is a high level exemplary flowchart showing one embodiment of aprocess by which bandwidth is shared between CCOs, particularly betweenneighbor networks operating in the coordinated mode. In this example,the source CCO initially determines one or more new time intervals thatit desires to reserve, i.e., to reserve as a reserved region or CFPregion (step 1010). In general, the source CCO derives or selects aschedule compatible with its other neighbor networks in its INL. Thesource CCO then sends a message/request to each of its neighbor networksin its INL indicating the requested additional time interval(s). In someembodiments, the schedule for each requested interval is specified by astart time and an end time, typically using the start time of thesender's beacon region as a reference (step 1020). Each of the neighbornetworks in general, particularly its CCO, responds to that request byeither accepting or rejecting that request (step 1024). If the neighbornetwork accepts that request, the neighbor central coordinator (NCO)typically changes its one or more regions to reflect the changes in itsschedule (step 1032). Such change may, for example, include changing oneor more time slots to a stayout period. If the neighbor network rejectsthat request, the neighbor network notifies the source CCO, typicallywith an unsuccessful result code, i.e., a rejection (step 1024).

When the source CCO receives the response from all of its neighbornetworks (NCOs) in its INL, it generally determines whether anyrejection responses have been received. If all the NCOs accepted therequested time interval (step 1040), the CCO updates a status fieldmessage, e.g., with a “Go,” and sends out a confirming message to all ofits neighbor networks in its INL and confirms that the source CCO isgoing to reserve the requested time interval (step 1060). On the otherhand, if any one of the NCOs rejected the request, (step 1040) thesource CCO updates the status field to a “Cancel,” informs the NCOs thatthe request has been cancelled or withdrawn. In some embodiments, theCCO typically sends this “Cancel” message only to those NCOs that havepreviously replied with successful result code or acceptance of therequest. Upon receiving the “Cancel” message, particularly these NCOsthat previously changed their regions reset their schedules to theiroriginal values (step 1052).

Releasing Bandwidth

A CCO that wishes to release one or more reserved time intervals, e.g.,one or more time slots in one or more reserved regions, typically sendsa release reserved time interval message to each neighbor CCO in itsINL. This release message typically contains the schedules to bereleased. The schedule is typically specified by a start and end time,for example, using the CCOs beacon region as a reference. Each CCO thatreceives this request typically sends a response back, e.g., a responseindicating success or failure. If a response indicating “success” isreceived, this means that the requesting CCO may change its previouslyindicated reserved region to CSMA, for example, while the CCO in the INLmay change its previous stayout region also to CSMA.

Shutting Down in Coordinated Mode

A CCO, e.g., called CCO SD, may inform or send a shut-down message,e.g., called in this example NN_REL_NET.IND, to the various neighbornetworks in its INL. This shut-down message typically specifies thebeacon slot being used by the CCO SD and the reserved regions allocatedto the CCO SD available that may now be released for use by neighborCCOs or by new CCOs. A CCO that receives this shut-down messagetypically sends a slot usage update message, e.g., calledNN_UPD_SLOTUSAGE.IND, to each CCO in its INL requesting it to set theappropriate bit in the slot usage field to “0.”

The CCOs in the INL that receive this NN_UPD_SLOTUSAGE.IND typicallyupdate their slot usage fields by changing the appropriate beacon slotto “0,” for example, and in turn also sends an NN_UPD_SLOTUSAGE.INDmessage to each NCO in its own INL that is in the same group and,typically, whose network ID is not the same as the network ID of the CCOwhich received the original shut-down message.

In some embodiments, if the last beacon slot in the beacon region hasbeen unoccupied for a period longer than a specified idle beacon slottimeout, a CCO may request to reduce the number of beacon slots. In oneembodiment, if a network operating in the coordinated mode shuts down,it may use an AC line sync count down field to indicate the beaconperiod within which it may stop transmitting. This may enable othercoordinating CCOs that are tracking the AC line cycle informationprovided by this departing CCO to recover appropriately, for example,CCOs tracking the AC line cycle information provided by departing CCOmay either choose a different CCO to track, if one is available, orstart tracking the AC Line cycle.

Detect-and-Report Procedure

The detect-and-report procedure is a process that enables a CCO todetermine whether a STA, particularly in its centralized network, iswithin the reception range of any ongoing transmissions. The CCOinitiates this procedure by requesting a STA to detect for ongoingtransmissions in some specified time intervals for a specified duration,i.e., when to listen and for how long. In some embodiments, the durationis defined in beacon periods. That STA then listens and detects for anytransmissions in the specified time interval(s) within those duration asinstructed and reports the results to the CCO. Using this process, a CCOmay be able to determine whether potential transmissions from that STAmay cause interference to any ongoing or future transmissions, as wellas whether any transmissions may potentially cause interference withthat STA.

FIG. 11 is another exemplary system 1100 that includes a group with twocentralized networks 1120, 1140. FIG. 12 shows exemplary beacon periods,B0 1270, B1 1272, B2 1274, BN 1278 divided into various time intervalsor time slots 1212, 1214, 1216, 1218, 1220, 1222, 1232, 1234, 1236,1238, 1240, 1242, 1252, 1254, 1256, 1258, 1260, 1262, 1282, 1284, 1286,1288, 1290, 1292. FIGS. 11 and 12 are discussed together.

In some embodiments, it is possible that the CCO of a centralizednetwork 1120, e.g., CCOA 1110, is not aware of the existence of aneighbor network, e.g., network B 1140/CCOB 1122. This may be due toseveral factors, e.g., the two CCOs, CCOA 1110 and CCOB 1122, are justphysically located too far apart from each other, hence they are unableto detect each other's beacons. In this exemplary embodiment, CCOA 1110and CCOB 1122 in general do not directly coordinate with each other. Thetwo CCOs 1110, 1122 are thus hidden from each other.

For illustrative purposes, let us assume that a STA in one of thenetworks, e.g., STA Z 1118, is able to detect the beacons of the othernetwork, e.g., network B 1140/CCOB 1122. STA Z, however, belongs tonetwork A 1120 and is managed by CCOA 1110. STA Z, for example, may bephysically located in between CCOA 1110 and CCOB 1122. In somesituations, when CCOA 1110 allocates a contention-free period timeinterval to STA Z, it is possible that the same time interval is alsobeing used by or allocated by network B 1140. CCOB 1122, for example,may use or allocate that same interval for CFP transmissions or CSMAtransmissions for its network 1140. In this exemplary embodiment, STA Z1118 thus may suffer interference from network B 1140.

A detect-and-report process may be implemented to address this issue. Ifthe topology table of CCOA 1110 indicates that STA Z is able to detectother outside networks, the CCOA 1110 may request STA Z todetect/monitor for any transmissions over certain time interval(s). Inthis embodiment, CCOA 1110 instructs other STAs, not shown, within itsnetwork 1120 to not transmit. This may be implemented, for example, byhaving CCOA 1110 specify reserved region(s) in that same timeinterval(s) when STA Z is detecting or monitoring for any transmissions.These reserved region(s), however, are not allocated to any STA in thenetwork 1120, thus, STA Z may freely listen for transmissions, which mayonly be generated by outside networks, i.e., not from network A, duringthose time intervals. These outside networks are non-coordinatingnetworks of network A 1120.

Referring to FIG. 12, CCOA 1110 may instruct STA Z to detect or monitorduring interval 1 and interval 3, i.e., INT1 1212, 1232 and INT3 1216,1236, of beacon periods B0 1270 and B1 1272. These same intervals 1212,1232, 1216, 1236 may be assigned by CCOA 1110 as reserved periods,intervals, or time slots for its own network A 1120, but not to any STAin the network 1120.

After the defined detecting intervals 1212, 1232, 1216, 1236 andduration/beacon periods, STA Z reports the results to the CCO. If STA Zreports that STA Z is able to detect transmissions during thosedetecting intervals 1212, 1232, 1216, 1236, CCOA 1110 may requestanother detect-and-report process at other time intervals, e.g.,interval 3 and interval 5 of beacon periods B2 and B7 (not shown), untilCCOA 1110, with the assistance of STA Z 1118, is able to find a timeinterval or intervals wherein there are no transmissions fromnon-coordinating networks.

If STA Z, however, reports and informs CCOA that STA Z did not detectany transmission during those detecting period(s), CCOA 1110 mayallocate that time intervals, interval 1 and interval 3, e.g., at somefuture beacon periods 1252, 1256, 1282, 1286, to STA Z.

FIG. 13 is an exemplary data flow showing how exemplary messages may beexchanged to implement the detect-and-report procedure. In general, theCCO, e.g., CCOA 1110, typically initiates this procedure by sending anexemplary CC_DETECT_REPORT.REQ 1304 message to a STA, e.g., STA Z 1118.The message may contain a field indicating the detecting duration(s),i.e., how long the detecting period is to last, and one or more globalidentifier (GLID) fields. Each GLID is typically associated with a startand end time—e.g., a time interval, thereby indicating when the detectedtime interval(s) are to occur. During those specified detect timeinterval(s), which may be contiguous or not contiguous with each other,the STA detects or listens for any ongoing transmissions.

After the defined detect time intervals(s), the STA then sends aresponse to the CCO via an exemplary CC_DETECT_REPORT.RSP message 1308,indicating the results of the detect-and-report procedure. This responsemessage 1308 may contain the type of transmissions (e.g., notransmissions, contention-free transmissions, and/or contention-basedtransmissions) that the STA detected during those detect time intervals.In some embodiments, the response may also include the signal level ofeach detected transmission and the bit loading estimate(s).

The detect-and-report procedure may also be useful in bandwidthallocation or scheduling. Upon receiving a connection request, for e.g.,via a global link set-up request (CC_LINK_NEW.REQ) message from a STA,if the topology table of the CCO indicates that the STA(s) requesting orassociated with the global link set-up request are able to detectstations in other networks that are not coordinating with the CCO, theCCO may request the STA(s) to perform the detect-and-report procedureover some specified detect time interval(s). If the STA(s) report thatcontention-free links or connections are not detected during the timeinterval(s), the CCO may allocate that same time interval(s) to the STAsand indicate to the STAs that request to send (RTS) and clear to send(CTS) messages may have to be transmitted/received. However, if theSTA(s) report that contention-free links are detected, this informationindicates that any potential transmissions from and by the STA(s) mayinterfere with the ongoing contention-free transmissions ofnon-coordinating networks and, therefore, the CCO may, if so decide, notto allocate that time interval to the STAs.

To ensure that a STA's CSMA transmissions do not interfere with CFPallocations of non-coordinating CCOs, in some embodiments, that STAs aretypically instructed to defer from transmitting during intervals in theCSMA allocation where CFP transmissions have been detected in previousbeacon periods.

Table V below shows exemplary fields of the exemplary detect-and-reportrequest message, e.g., CC_DETECT_REPORT.REQ.

TABLE V Exemplary CC_DETECT_REPORT.REQ Message Field Exemplary OctetSize Field Number (Octets) Definition Duration 0 1 Amount of time todetect for ongoing transmissions, in units of number of Beacon Periods.“00” = zero Beacon Periods, “01” = one Beacon Period, and so on NumGLID1 1 The number of GLID fields in this message (=N). The maximum valuefor this field is 8. “00” = none “01” = one, and so on Each GLID isassociated with a start and end time. GLID[1] 2 1 The first GLID toperform the detect-and- report procedure. . . . . . . . . . . . .GLID[N] N + 1 1 The last GLID to perform the detect-and- reportprocedure.

Table VI below shows exemplary fields of the exemplary detect-and-reportresponse message, e.g., CC_DETECT_REPORT.RSP.

TABLE VI Exemplary CC_DETECT_REPORT.RSP Message Field Exemplary OctetSize Field Number (Octets) Definition NumGLID 0 1 Number of GLIDInfo()in this message (=N). “00” = none “01” = one, and so on GLIDInfo[1] 1-66 Information about the first GLID (see Table VII) . . . . . . . . . . .. GLIDInfo[N] — 6 Information about the last GLID (see Table VII)

Table VII below shows exemplary format of a GLIDInfo field.

TABLE VII Exemplary GLIDInfo Format Exemplary Octet Field Size FieldNumber (Octets) Definition GLID 0 1 GLID corresponding to this GLIDInfo[]. CFDetected 1 1 “00” = Contention-free Frame Controls are notdetected. “01” = Contention-free Frame Controls are detected.CSMADetected 2 1 “00” = Contention-based Frame Controls are notdetected. “01” = Contention-based Frame Controls are detected.OthersDetected 3 1 “00” = other unknown types of transmissions are notdetected. “01” = other unknown types of transmissions are detected.Signal Level 4 1 “00” = information not available “01” = signal levelis >−10 dB, but ≦0 dB (relative to full transmit power, −50 dBm/Hz) “02”= signal level is >−15 dB, but ≦−10 dB “03” = signal level is >−20 dB,but ≦−15 dB . . . “08” = signal level is >−75 dB, but ≦−70 dB “09” =signal level is <−75 dB Average BLE 5 1 Average BLE. Average BLE may beestimated based on Discover Beacon reception. This field is typicallyset to zero if not provided. Providing a non-zero value is optional.

FIG. 14 is a high-level block diagram of an exemplary centralcoordinator 1400 according to an embodiment of the invention. In someembodiments, the central coordinator 1400 includes a beacon slotallocation module 1402, a group coordination mode module 1406, an ACline cycle synchronization module 1410, a network operating module 1414,and a beacon decoding module 1418. In some embodiments, a bus 1422connects the various interface modules. In some embodiments, an I/Ointerface 1426 couples the CCO 1400 to the network, enablingcommunication with other devices in the network. In general, the beaconslot allocation module 1402 allocates one or more beacon slots, andassociates each of the beacon slots to a unique network, such that thereis typically a one-to-one correspondence between the number of beaconslots and the number of networks in a group operating in the coordinatedmode. Each network in the coordinated mode thus has a unique beacon slotto transmit its own beacon or beacons. The beacon slot allocation module1402 also performs the function of increasing as well as decreasing theallocated beacon slots, which may be in response to requests by otherCCOs.

The AC line cycle synchronization module 1410 typically tracks andmonitors the AC line cycle, sets appropriate fields, and synchronizesthe various networks to the AC line cycle, if appropriate. The networkoperating mode module 1414 determines the operating mode a networkshould use, including transitions between the coordinated mode anduncoordinated mode, and vice versa. The beacon decoding module 1418typically detects and decodes beacons. The group coordination module1406 performs the functions related to the coordination of two of moregroups of networks, for example, by allocating one or more protectedregions in a beacon.

In some embodiments, not shown, a device, e.g., a station and/or acentral coordinator, may include a detect-and-report procedure modulethat performs the features of the detect-and-report procedure discussedabove.

Although this invention has been disclosed in the context of certainembodiments and examples, it will be understood by those skilled in theart that the present invention extends beyond the specifically disclosedembodiments to other alternative embodiments and/or uses of theinvention and obvious modifications and equivalents thereof. Inaddition, while a number of variations of the invention have been shownand described in detail, other modifications, which are within the scopeof this invention, e.g., order of steps may be changed, will be readilyapparent to those of skill in the art based upon this disclosure. It isalso contemplated that various combinations or subcombinations of thespecific features and aspects of the embodiments may be made and stillfall within the scope of the invention. Accordingly, it should beunderstood that various features and aspects of the disclosedembodiments can be combined with or substituted for one another in orderto form varying modes of the disclosed invention. Thus, it is intendedthat the scope of the present invention herein disclosed should not belimited by the particular disclosed embodiments described above.

1. A method of synchronizing one or more networks in a first group, eachof the one or more networks comprising a central coordinator, eachcentral coordinator adapted to operate in an operating mode selectedfrom a group consisting of uncoordinated mode and coordinated mode, eachcentral coordinator adapted to transition from the uncoordinated mode tothe coordinated mode or from the coordinated mode to the uncoordinatedmode, the method comprising the steps of: allocating one or more beaconslots wherein each of the allocated one or more beacon slots isassociated with a unique network from the one or more networks in thefirst group; transmitting at least one beacon at the allocated beaconslot by the associated network, wherein the at least one beaconcomprises network allocation and scheduling information; wherein oneslot of the one or more beacon slots is a master slot synchronized to analternating current (AC) line cycle functioning as a master timingsequence; detecting one or more beacons; decoding the one or moredetected beacons; and transitioning, by the central coordinator of atleast one of the one or more networks in the first group, from thecoordinated mode to the uncoordinated mode or from the uncoordinatedmode to the coordinated mode based on the one or more beacons detected;wherein the coordinated mode is associated with distinct time slots. 2.The method of claim 1 wherein the transmitting step is over a power linemedium.
 3. The method of claim 1 wherein at least one of the one or morebeacon slots that is not the master slot is synchronized to the AC linecycle based on the master slot.
 4. The method of claim 1 furthercomprising the step of: allocating an additional beacon slot associatedwith a new network joining the first group.
 5. The method of claim 1further comprising the step of: releasing one of the allocated beaconslots, wherein the released beacon slot is adapted to be used by anincoming new network.
 6. The method of claim 1 further comprising thestep of: coordinating the first group with a second group, wherein thesecond group comprises one or more second group networks.
 7. The methodof claim 1 wherein the master slot is synchronized to the AC line cycleby determining a point in the AC line cycle.
 8. The method of claim 1wherein the AC line cycle is synchronized with a digital phase lockedloop detection.
 9. The method of claim 1, wherein the master slot issynchronized to the AC line cycle by determining a point in the AC linecycle and an offset.
 10. The method of claim 1 wherein the step ofallocating one or more beacon slots includes updating one or more slotusage fields.
 11. The method of claim 1 further comprising the step of:determining a location of one future beacon based on the AC line cycle.12. The method of claim 1 further comprising the step of: determiningwhen one of the one or more networks is shutting down based on the ACline cycle.
 13. The method of claim 1 wherein the one or more beaconslots are scheduled within a beacon region with a defined number ofbeacon slots.
 14. The method of claim 1 wherein the one or more beaconslots are scheduled within a beacon region with a variable number ofbeacon slots.
 15. A device comprising: a beacon slot allocation moduleadapted to: allocate one or more beacon slots, wherein each of theallocated one or more beacon slots are each associable with arespectively unique network, each unique network comprising a centralcoordinator, and wherein one slot of the one or more beacon slots is amaster slot synchronized to an alternating current (AC) line cyclefunctioning as a master timing sequence; and release an allocated one ormore beacon slots, wherein the released beacon slot is adapted to beassociated with another new network; an alternating current (AC) linecycle synchronization module adapted to: monitor the AC line cycle; andsynchronize at least one of the allocated one or more beacon slots tothe AC line cycle; a beacon decoding module adapted to: decode one ormore detected beacons; a network operating mode module adapted to:determine, based on at least one of the decoded one or more beacons, thenetwork operating mode selected from a group consisting of coordinatedmode and uncoordinated mode; wherein coordinated mode associated withdistinct time slots; and transition, from the coordinated mode to theuncoordinated mode or from the uncoordinated mode to the coordinatedmode based on the one or more beacons detected.
 16. The device of claim15 further comprising: a group coordination module adapted to coordinateone or more groups.
 17. The device of claim 15 adapted to communicateover a power line network medium.
 18. A system comprising: one or morenetworks in a first group; wherein each network comprises a centralcoordinator controlling its corresponding network; wherein each networkis configured to operate in a mode selected from a group consisting of acoordinated mode and an uncoordinated mode and is configured totransition between a coordinated mode and an uncoordinated mode, whereinthe coordinated mode is associated with distinct time slots; each of thecentral coordinators adapted to decode one or more detected beacons;each of the central coordinators adapted to allocate one or more beaconslots within a beacon region, wherein each of the allocable one or morebeacon slots is associable with a unique network from the one or morenetworks, and wherein at least one of the one or more beacon slots is amaster slot synchronized to an alternating current line cyclefunctioning as a master timing sequence; and a power line communicationnetwork medium operably coupled to the one or more networks.
 19. Thesystem of claim 18 wherein the one or more beacon slots within thebeacon region is a variable number of beacon slots.